Because they do not corrode, are light weight, and are easy to clean, unlike metal conveyor belts, plastic conveyor belts are used widely, especially in materials handling and conveying food products. Modular plastic conveyor belts are made up of molded plastic modular links, or belt modules, that can be arranged side by side in rows of selectable width. A series of spaced apart link ends extending from each side of the modules include aligned apertures to accommodate a pivot rod. The link ends along one end of a row of modules are interconnected with link ends of an adjacent row. A pivot rod journaled in the aligned apertures of the side-by-side and end-to-end connected modules forms a hinge between adjacent rows. Rows of belt modules are then connected together to form an endless conveyor belt capable of articulating about a drive sprocket.
The retention of the pivot rod is an important feature of the modular plastic conveyor belts. Rod retention can be accomplished by enlarging the heads of the pivot rods at both ends but such would not allow for disassembly without destroying the rod head. Headless rods have been used for easier production and belt assembly. These type of rods must be blocked at both ends of the belt during use. In addition headless rods are often difficult to remove for disassembly.
One approach to rod retention is to have a head at one end of a rod and a headless section at the opposite end. The headed rod is furnished with a rod retaining ring disposed on the shaft at a distance from the head portion of the rod. The rod is inserted through the pivot holes of the module links, which are all exactly the same diameter. The retaining ring is just a little bit larger in diameter than the pivot hole of the outermost link, such that the ring may be forced through the pivot hole of the outermost link end and is able to expand behind the link. In this arrangement the rod is kept firmly in position by the retaining ring. The system described above has the drawback that it requires tight tolerances of the hole diameter of the outermost link and the retaining ring diameter. In practice, there is a risk that the rod does not retain well enough or is retained tightly and cannot be easily disassembled. In addition, if the retaining ring is a little too large, it may be sheared off when inserted.
What is needed is a device that makes the above-described tolerances less critical.